The present invention relates to electronic displays and, in particular, to electrodes that protect displays from deterioration, their mode of use and their methods of fabrication.
Electrophoretic displays have been the subject of intense research and development for a number of years. Electrophoretic displays have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread usage. For example, particles that make up such displays tend to cluster and settle, resulting in inadequate service-life for these displays.
An encapsulated, electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates.
Traditionally, electronic displays such as liquid crystal displays have been made by sandwiching an optoelectrically active material between two pieces of glass. In many cases each piece of glass has an etched, clear electrode structure formed using indium tin oxide (xe2x80x9cITOxe2x80x9d). A first electrode structure controls all the segments of the display that may be addressed, that is, changed from one visual state to another. A second electrode, sometimes called a counter electrode, addresses all display segments as one large electrode, and is generally designed not to overlap any of the rear electrode wire connections that are not desired in the final image. Alternatively, the second electrode is also patterned to control specific segments of the displays. In these displays, unaddressed areas of the display have a defined appearance.
In electrophoretic displays, it has been commonly observed that the display fails after some time. One of the reasons why such a display may fail is that the materials is used to construct the display are damaged by repeated application of electrical addressing signals. Another reason why such displays fail is that the display elements or electrodes suffer mechanical or electrochemical damage.
In one aspect the invention provides novel apparatus and methods for providing protective electrodes for use in electrically addressable displays including electrophoretic displays. Additionally the invention discloses applications of these methods and materials in displays that can be flexible, that can be applied in large area, low cost, and high durability applications that operate under a variety of environments.
In one aspect, the present invention relates to a display that includes a display element capable of changing its appearance in response to an electric field, and a first electrode adjacent the display element, such that the first electrode provides a protective layer adapted to prevent mechanical or electrochemical damage to the display element
In one embodiment, the display includes an electrophoretic display element that has as components a capsule, a dispersing fluid having a first optical property disposed within the capsule, and at least one electrophoretically-mobile particle disposed within the capsule. The at least one electrophoretically-mobile particle has a second optical property different from the first optical property, and the at least one electrophoretically-mobile particle can change position within the capsule under the influence of an applied electric field. The appearance of the display element can change depending on where the at least one electrophoretically-mobile particle is situated within the capsule.
In other embodiments, the protective layer is flexible, and the protective layer is adapted to prevent mechanical removal of the electrophoretic element from the display. In yet another embodiment, the protective layer includes a plurality of conductors extending therethrough. In still another embodiment, the first electrode is transparent and the protective layer is disposed upon the transparent electrode, the protective layer being capable of protecting the transparent electrode from degradation under the application of an electrical potential. In a further embodiment, the first electrode is transparent and comprises one or more oxides selected from the group consisting of indium oxide, tin oxide and indium tin oxide.
In another embodiment, the protective layer comprises at least one chemical composition selected from the group consisting of the metals nickel, palladium, platinum, ruthenium, rhodium, silver, aluminum, gold, titanium, chromium and zinc, and the oxides silver oxide (AgO), aluminum oxide (Al2O3), gold (III) oxide (Au2O3), titanium (II) oxide (TiO), titanium (IV) oxide (TiO2), chromium (III) oxide (Cr2O3), chromium (VI) oxide (CrO3), zinc oxide (ZnO), nickel (II) oxide (NiO), palladium (II) oxide (PdO), platinum (IV) oxide (PtO2), ruthenium (IV) oxide (RuO2), and rhodium (III) oxide (Rh2O3). In a preferred embodiment, the protective layer comprises palladium. In still another embodiment, the protective layer has a thickness not greater than approximately 10 nm.
In another aspect, the invention relates to a display, that includes a display element, and a vapor-permeable electrode adjacent the display element. In one embodiment, the display includes an electrophoretic display element that has as components a capsule, a dispersing fluid having a first optical property disposed within the capsule, and at least one electrophoretically-mobile particle disposed within the capsule. The at least one electrophoretically-mobile particle has a second optical property different from the first optical property, and the at least one electrophoretically-mobile particle can change position within the capsule under the influence of an applied electric field. The appearance of the display element can change depending on where the at least one electrophoretically-mobile particle is situated within the capsule.
In another embodiment, the vapor-permeable electrode comprises an electrode permeable to water vapor. In another embodiment, the vapor-permeable electrode comprises a reticulated electrically conductive structure. The reticulated electrically conductive structure can be a wire mesh. The wire mesh can be made of copper or bronze, as well as other metals. The reticulated electrically conductive structure can be a reticulated layer at least partially coated with an electrically conductive material, or it can be a reticulated layer at least partially impregnated with an electrically conductive material.
In another aspect the invention relates to an electrostatically addressable display, including a display element having a first surface and a second surface, a protective layer disposed adjacent the first surface of the display element, the protective layer capable of transmitting charge, and an electrode disposed adjacent the second surface of the display element.
In one embodiment, the protective layer is flexible. In one detailed embodiment, the protective layer comprises an anisotropic material. For example, the protective layer can comprise a sheet of plastic and a plurality of conductive elements vertically embedded in the sheet. The conductive elements can comprise a plurality of rods. The conductive elements can be substantially invisible. Alternatively, the protective layer can comprise a semiconductor. For example, the protective layer can comprise a polymeric semiconductor including a plurality of photoconductors. The protective layer can is comprise a layer of polymeric material, such as Mylar.
In another embodiment, the display includes an electrophoretic display element that has as components a capsule, a dispersing fluid having a first optical property disposed within the capsule, and at least one electrophoretically-mobile particle disposed within the capsule. The at least one electrophoretically-mobile particle has a second optical property different from the first optical property, and the at least one electrophoretically-mobile particle can change position within the capsule under the influence of an applied electric field. The movement of the at least one electrophoretically-mobile particle within the capsule changes the appearance of the display element.
In another embodiment, the application of an electrostatic voltage of less than 1000 volts across the display creates an electrostatic voltage of at least 5 volts across the electrophoretic element. In still another embodiment the protective layer disposed adjacent the first surface of the capsule comprises a layer having a resistivity less than 1012 ohm-centimeters and the electrophoretic element comprises a material having a resistivity greater than 1012 ohm-centimeters. In yet another embodiment, the protective layer comprises a material having a resistivity greater than a resistivity of the electrophoretic element and a thickness that is not more than 20% of the thickness of a layer of the electrophoretic elements, whereby a resistance of the protective layer is approximately 20% of a resistance of the electrophoretic element. In a further embodiment, the protective layer disposed adjacent the first surface of the display element comprises a layer of polymeric material. In still another embodiment, the protective layer disposed adjacent the first surface of the display element comprises a layer that conducts charge in a direction substantially perpendicular to the layer. In an additional embodiment, the protective layer disposed adjacent the first surface of the display element comprises a layer of an insulating material having a plurality of conductive structures extending therethrough. In yet a further embodiment, the protective layer disposed adjacent the first surface of the display element comprises a first region having a first resistivity and a second region having a second resistivity.
In a still further embodiment, the first region having a first resistivity and the second region having a second resistivity comprise a material which is doped differently within the first region and the second region. In one detailed embodiment, the first region comprises a first material and the second region comprises a second different material. In another embodiment, the less conductive of the first and the second regions is continuous and surrounds an array of isolated segments of the more conductive of the first and the second regions. In a further embodiment, the less conductive of the first and the second regions comprises vias providing access to the array of isolated segments. In an alternative embodiment, the less conductive of the first and the second materials comprises a region that is continuous and that surrounds an array of islands of the more conductive of the first and the second materials, and the less conductive of the first and the second materials comprises pinholes providing access to the array of islands. The plurality of pinholes can comprise pinholes large enough to receive a print head. The array of islands can form a visible array of pixels when actuated by an electrostatic print head. In another example, the protective layer has a first surface and a second surface, and the second surface of the protective layer comprises the array of islands in electrical communication with the first surface of the electrophoretic material layer. The array of islands can be in physical contact with the electrophoretic material. The protective layer can comprise one or more vias providing access to the array of islands. The protective layer can comprise one or more pinholes providing access to the array of islands. The pinholes form an array which correspond to the array of islands.
In another embodiment, the protective layer disposed adjacent the first surface of the display element comprises a first region having a first resistivity and a plurality of regions having a second resistivity. In yet a further embodiment, the plurality of regions having a second resistivity comprises arrays of three islands.
In yet another embodiment, the protective layer comprises a substrate having a coating of a substantially transparent radiation responsive charge emitting material disposed on a surface. The coating can be light or heat responsive. The surface having the coating can be disposed adjacent the electrophoretic material.
In yet another embodiment, the protective layer comprises an anisotropic conductor. In one detailed embodiment, the anisotropic conductor comprises a substantially linear array of colloidal metal spheres. The substantially linear array can be substantially perpendicular to a plane of the protective layer. In one example, the colloidal metal spheres are substantially closely packed to form a vertical conductive path. In another example, the colloidal metal spheres are partially closely packed to form a vertical conductive path when compressed. The colloidal metal spheres can be compressed with a stylus or a print head.
In still another embodiment, the step of providing the protective layer can comprise coating a substrate with a substantially transparent radiation responsive charge emitting material. In one example, providing the protective layer can comprise coating a substrate with a substantially transparent light responsive charge emitting material. In another example, providing the protective layer can comprise coating a substrate with a substantially transparent heat responsive charge emitting material. In yet another embodiment, the step of providing the protective layer comprises placing a layer of conductive material on a substrate and etching portions of the layer to form an array of islands.
In another aspect the invention relates to a method of addressing an electrostatically addressable display element, comprising steps (a) through (e). Step (a) involves providing an electrophoretic element. The electrophoretic element includes a capsule, a dispersing fluid having a first optical property disposed within the capsule, and at least one electrophoretically-mobile particle disposed within the capsule. The at least one electrophoretically-mobile particle has a second optical property different from the first optical property, and the at least one electrophoretically-mobile particle can change position within the capsule under the influence of an applied electric field. The movement of the at least one electrophoretically-mobile particle within the capsule changes the visual appearance of the display element. Steps (b) through (e) involve: (b) providing a protective layer disposed adjacent the capsule, the protective layer adapted to to transmit charge, (c) providing a first electrode disposed adjacent the capsule, (d) disposing adjacent the protective layer an addressing electrode, and (e) activating the addressing electrode in conjunction with the first electrode to subject the electrophoretic element to a selected one of the first applied electric field and the second applied electric field produced between the first electrode and the addressing electrode so as to address the electrophoretic element. The method of addressing a display can involve addressing with an electrostatic print head having a first electrodes
In one embodiment, step (b) comprises providing a layer of an insulating material having a plurality of conductive structures disposed therethrough, and step (e) comprises activating the addressing electrode in conjunction with the first electrode by touching at least one of the conductive structures so as to apply a selected one of the first applied electric field and the second applied electric field produced between the first electrode and the conductive structure so as to address the electrophoretic element
In another embodiment, step (b) comprises providing a layer of a material having a more resistive region and a less resistive region, the less resistive region comprising at least one island adjacent the electrophoretic element, the more resistive region having at least one pinhole therethrough, the at least one pinhole providing access to the at least one island of more conductive material, and step (e) comprises activating the addressing electrode in conjunction with the first electrode by emitting charge that passes through the at least one pinhole so as to apply a selected one of the first applied electric field and the second applied electric field produced between the first electrode and the at least one island so as to address the electrophoretic element.
In another embodiment the invention provides a display comprising an electrophoretic display element capable of changing its appearance in response to an electric field; and a protective layer secured to this display element, adapted to prevent mechanical damage thereto and capable of transmitting charge to the display element. Preferably, this display element is essentially laminar having opposed first and second surfaces and protective layers are secured to both the first and second surfaces.